Solution Combustion Synthesis of Ni-Based Nanocatalyst Using Ethylenediaminetetraacetic Acid and Nickel-Carbon Nanotube Growth Behavior.

We studied the influence of the ethylenediaminetetraacetic acid (EDTA) content used as combustion fuel when fabricating nickel oxide (NiO) nanocatalysts via solution combustion synthesis, as well as the growth behavior of carbon nanotubes (CNTs) using this catalyst. Nickel nitrate hexahydrate (Ni(NO3)2∙6H2O) was used as the metal precursor (an oxidizer), and the catalysts were synthesized by adjusting the molar ratio of fuel (EDTA) to oxidizer in the range of 1:0.25 to 2.0. The results of the crystal structure analysis showed that as the EDTA content increased beyond the chemical stoichiometric balance with Ni(NO3)2∙6H2O (F/O = 0.25), the proportion of Ni metal within the catalyst particles decreased, and only single-phase NiO was observed. Among the synthesized catalysts, the smallest crystallite size was observed with a 1:1 ratio of Ni ions to EDTA. However, an increase in the amount of EDTA resulted in excessive fuel supply, leading to an increase in crystallite size. Microstructure analysis revealed porous NiO agglomerates due to the use of EDTA, and differences in particle growth based on the fuel ratio were observed. We analyzed the growth behavior of CNTs grown using NiO nanocatalysts through catalytic chemical vapor deposition (CCVD). As the F/O ratio increased, it was observed that the catalyst particles grew excessively beyond hundreds of nanometers, preventing further CNT growth and leading to a rapid termination of CNT growth. Raman spectroscopy was used to analyze the structural characteristics of CNTs, and it was found that the ID/IG ratio indicated the highest CNT crystallinity near an F/O ratio of 1:1.

Phase Stability and Slag-Induced Destabilization in MnO2 and CeO2-Doped Calcia-Stabilized Zirconia.

MnO2 and CeO2 were doped to improve the corrosion resistance of CSZ (calcia-stabilized zirconia), and we studied the phase formation, mechanical properties, and corrosion resistance by molten mold flux. The volume fraction of the monoclinic phase gradually decreased as the amount of MnO2 doping increased. The splitting phenomenon of the t(101) peak was observed in 2Mn_CSZ, and in 4Mn_CSZ, it was completely split, forming a cubic phase. The relative density increased and the monoclinic phase decreased as the doping amount increased, leading to an increase in Vickers hardness and flexural strength. However, in 3Mn_CSZ and 4Mn_CSZ, where cubic phase formation occurred, the tetragonal phase decreased, leading to a reduction in these properties. MnO2-doped CSZ exhibited a larger fraction of the monoclinic phase compared to the original CSZ after the corrosion test, indicating worsened corrosion resistance. These results are attributed to the predominant presence of Mn3+ and Mn2+ forms, rather than the Mn4+ form, which has a smaller basicity difference with SiO2, and due to the low melting point. The monoclinic phase fraction decreased as the doping amount of CeO2 increased in CeO2-doped CSZ, but the rate of decrease was lower compared to MnO2-doped CSZ. The monoclinic phase decreased as the doping amount increased, but the Vickers hardness and flexural strength showed a decreasing trend due to the low relative density. The destabilization behavior of Ca in SEM-EDS images before and after corrosion was difficult to identify due to the presence of Ca in the slag, and the destabilization behavior of Ce due to slag after corrosion was not observed. In the XRD data of the specimen surface after the corrosion test, the fraction of the monoclinic phase increased compared to before the test but showed a lower monoclinic phase fraction compared to CSZ. It is believed that CeO2 has superior corrosion resistance compared to CaO because Ce predominantly exists in the form of Ce4+, which has a smaller difference in basicity within the zirconia lattice.

Oxygen Vacancy Ordering and Molten Salt Corrosion Behavior of ZnO-Doped CeYSZ for Solid Oxide Membranes.

Although 4Ce4YSZ has high corrosion resistance, it faces challenges concerning its sinterability and ionic conductivity. Therefore, we studied destabilization behavior caused by corrosion and oxygen vacancy ordering according to ZnO doping. Powders of (4Ce4YSZ)1-x(ZnO)x (x = 0.5, 1, 2, 4 mol%) were synthesized using the sol-gel method. With the addition of ZnO, the cubic phase increased, and secondary phases were not observed. The (111) peak showed a higher angle shift in ZnO-doped 4Ce4YSZ compared to 4Ce4YSZ, and TEM-SAED revealed a reduction in the spacing of the (011)t plane, suggesting lattice contraction due to the substitution of the smaller Zn2+ (60 Å) for Zr4+ (84 Å) in the lattice. The local atomic structure analysis was conducted using EXAFS to investigate the oxygen vacancy ordering behavior. Zr K-edge Fourier transform data revealed a decrease in the Zr-O1 peak intensity with an increasing amount of ZnO doping, indicating an increase in oxygen vacancies. The Zr-O1 peak position shifted to the right, leading to an increase in the Zr-O1 interatomic distance. In the Y K-edge Fourier transform data, the Y-O1 peak intensity did not decrease, and there was little variation in the Y-O1 interatomic distance. These results suggest that the oxygen vacancies formed due to ZnO doping are located in the neighboring oxygen shell of Zn, rather than in the neighboring oxygen shells of Y and Zr. Impedance measurements were conducted to measure the conductivity, and as the amount of ZnO doping increased, the total conductivity increased, while the activation energy decreased. The increase in oxygen vacancies by ZnO doping contributed to the enhancement of conductivity, and it is considered that these created oxygen vacancies did not interact with Zn2+ and did not form defect associations. Fluoride-based molten salts were introduced to the specimens to assess the corrosion behavior in a molten salt environment. Yttrium depletion layers (YDLs) were formed on the surfaces of all specimens due to the leaching of yttrium. However, Ce remained relatively stable at the interface according to EDS line scans, suggesting a reduction in the phase transformation (cubic, tetragonal to monoclinic) typically associated with yttrium leaching in YSZ.

Enhancing the Plasma-Resistance Properties of Li2O-Al2O3-SiO2 Glasses for the Semiconductor Etch Process via Alkaline Earth Oxide Incorporation.

To develop plasma-resistant glass materials suitable for semiconductor etching processes, we introduced alkaline earth oxides (ROs) into a Li2O-Al2O3-SiO2 (LAS) glass. Analysis of glass properties with respect to the additives revealed that among the analyzed materials, the LAS material in which Li2O was partially replaced by MgO (MLAS) exhibited the most favorable characteristics, including a low dielectric constant (6.3) and thermal expansion coefficient (2.302 × 10-6/°C). The high performance of MLAS is attributed to the high ionic field strength of Mg2+ ions, which restricts the movement of Li+ ions under the influence of electric fields and thermal vibrations at elevated temperatures. When exposed to CF4/O2/Ar plasma, the etching speed of RO-doped glasses decreased compared with that of quartz and LAS glass, primarily owing to the generation of a high-sublimation-point fluoride layer on the surface. Herein, MLAS demonstrated the slowest etching speed, indicating exceptional plasma resistance. X-ray photoelectron spectroscopy analysis conducted immediately after plasma etching revealed that the oxidation-to-fluorination ratio of Li was the lowest for MLAS. This observation suggests that the presence of Mg2+ ions in the plasma discharge inhibits the migration of Li+ ions toward the surface, thereby contributing to the excellent plasma resistance of MLAS.

Destabilization and Ion Conductivity of Yttria-Stabilized Zirconia for Solid Oxide Electrolyte by Thermal Aging.

The degradation behavior of yttria-stabilized zirconia by thermal aging was investigated in terms of phase transformation, local atomic structure, and electrical conductivity. The average grain size of 8YSZ was increased from 20.83 µm to 25.81 µm with increasing aging temperature. All 8YSZ samples degraded at different temperatures had a predominantly cubic structure. The (400) peak of 8YSZ deteriorated at 1300 and 1400 °C shifted to a high angle, and the peak of tetragonal was not indexed. For 8YSZ degraded at 1500 °C, the (400) peak shifted to a lower angle, and the peak of tetragonal was identified. Analysis of the local microstructure of aged 8YSZ using extended X-ray absorption fine structure showed that the intensity of the Zr-O peak gradually increased and that the intensity of the peak of cationic Zr decreased as the aging temperature increased. The changes in the peaks indicate that the oxygen vacancies were reduced and Y3+ ions escaped from the lattice, leading to the destabilization of 8YSZ. The activation energies of 8YSZ at 1300 °C and 1400 °C were derived to be 0.86 and 0.87 eV, respectively, and the activation energy of 8YSZ at 1500 °C increased significantly to 0.92 eV. With the thermal deterioration of 8YSZ, the cation (Y3+) escaped from the lattice and the number of oxygen vacancies decreased, resulting in the formation of a tetragonal structure and high activation energy at 1500 °C.

Fabrication of Highly Porous and Pure Zinc Oxide Films Using Modified DC Magnetron Sputtering and Post-Oxidation.

Porous films of metals and metal oxides exhibit larger surface areas and higher reactivities than those of dense films. Therefore, they have gained growing attention as potential materials for use in various applications. This study reports the use of a modified direct current magnetron sputtering method to form porous Zn-ZnO composite films, wherein a subsequent wet post-oxidation process is employed to fabricate pure porous ZnO films. The porous Zn-ZnO composite films were initially formed in clusters, and evaluation of their resulting properties allowed the optimal conditions to be determined. An oxygen ratio of 0.3% in the argon gas flow resulted in the best porosity, while a process pressure of 14 mTorr was optimal. Following deposition, porous ZnO films were obtained through rapid thermal annealing in the presence of water vapor, and the properties and porosities of the obtained films were analyzed. An oxidation temperature of 500 °C was optimal, with an oxidation time of 5 min giving a pure ZnO film with 26% porosity. Due to the fact that the films produced using this method are highly reliable, they could be employed in applications that require large specific surface areas, such as sensors, supercapacitors, and batteries.

[Epidemiologic investigation on an outbreak of salmonellosis in Yeongcheon-si, 2004].

OBJECTIVES: An outbreak of salmonellosis occurred among the students and staff of D primary school in Yeongcheon-si, 2004. This investigation was carried out to prevent any recurrence of this outbreak and to study the infection source and transmission of the salmonellosis. METHODS: The authors conducted a questionnaire survey among 1,205 students and staff members from D primary school about the ingestion of the school lunch and drinking water, and the manifestation of their symptoms. The author examined rectal swabs, the tap water and microorganism cultures, and we also investigated the dining facility and water supply facility. RESULTS: The diarrheal cases were defined as the confirmed cases or the persons who had diarrhea more than one time with symptoms such as fever, vomiting and tenesmus. The diarrheal attack rate was 28.0%. Ingestion of fried bean curd with egg had a significantly high association with the diarrheal attack rate (p<0.05), and the relative risk of the fried bean curd with egg was 10.68 (95% CI=3.88-29.41), as was determined by logistic regression analysis. The bacterial counts in the tap water of the food preparation room and toilet (first floor) exceeded the maximum permissible counts. S. Enteritidis bacteria were only cultured from the fried bean curd with egg of all the supplied foods on September 3, 2004. CONCLUSIONS: The major cause of salmonellosis was presumed to be the contaminated bean curd via contaminated tap water due to a water leak of a school water pipe. This contaminated bean curd was under prepared, which allowed the S. Enteritidis to survive and multiply prior to its ingestion.

[Investigation of a series of brucellosis cases in Gyeongsangbuk-do during 2003-2004].

OBJECTIVES: We conducted an investigation on 14 cases of brucellosis in Gyeongsangbuk-do during 2003-2004 to understand the source of infection and the transmission routes of brucellosis. METHODS: The authors visited the each of the health centers and we examined the patients, their written epidemiologic questionnaire and the occurrence of bovine brucellosis. We visited the patients' living and work areas, and we examined their occupations, the date they developed symptoms, the progress of their symptoms, whether or not they were treated, their current status, whether or not they consumed raw milk and raw meat, and if their work was related to cattle breeding and the related details. We reviewed the results of the blood tests and medical records and we examined the cattle's barn. RESULTS: There were 3 patients in 2003 and 11 patients in 2004. All of their brucella antibody titer exceeded 1:160. The patients' symptoms were fever, myalgia, malaise, chills and an influenza-like illness, but the clinical signs were absent on the medical records. Brucella abortus were cultured from 3 of the patients' blood samples. CONCLUSIONS: When the authors discovered the transmission routes, they were divided into 4 different sorts. The first route was related to cattle birth such that patients touched the calves or placentas that were infected with the Brucella species. The second route was related to performing artificial insemination on the cattle and the semen that was used for artificial insemination. The third route was due to the ingestion of raw meat and milk. The last route was due to sexual intercourse between the patients.